"reverse" magnetostriction effects in the [001] shape magnetostriction of cexLa1-xSb and smxLa1-xSb single crystals

Shape magnetostriction measurements along the [001] direction were carried out for all the magnetic rare-earth ions, R, in RxLa1-xSb. At low temperatures the magnetostriction of both Ce and Sm are "reversed" with respect to the high temperatures. A crystal-field model can explain this phenomenon by the sign reversal of the expectation value of the quadrupole operator O^20. The data are consistent with a negative second-order magnetoelastic coupling constant, V23, for all the rare-earth ions.